OBJECTIVES To assess the association between amyotrophic lateral sclerosis (ALS) and previous traumatic events, age of trauma, and site of injury. METHODS A population-based case-control study was performed in five European countries (Italy, Ireland, France, United Kingdom, Serbia). Newly diagnosed ALS patients and matched controls were interviewed to collect relevant demographic factors and exposures. Key clinical features at diagnosis were collected in ALS patients. Trauma was any accidental event causing an injury. Injuries were dated and classified according to cause, severity, type, site, and complications. All exposures were censored five years before symptoms onset. Risks were computed as odds ratios (OR) with 95% confidence intervals (CI) using univariate and multivariate conditional logistic regression models. RESULTS Five hundred and seventy-five ALS patients and 1150 controls were interviewed. Disabling traumatic events predominated in the cases (OR 1.54 (95% CI 1.24-1.92)) and maintained significance after adjustment, with a significant gradient. A history of 2 + head injuries was associated with an almost three-fold increased risk of ALS. The risk was almost two-fold when trauma occurred at age 35-54 years. Site of injury was uneventful. CONCLUSIONS Traumatic events leading to functional disability or confined to the head are risk factors for ALS. Traumatic events experienced at age 35-54 years carry the highest risk.